it has been hypothesized that part of the etiology of alcoholism may be linked to aberrant fatty acid and prostaglandin metabolism, based primarily upon the finding that behavioral effects of ethanol can be modulated by preadministration of prostaglandin synthetase inhibitors. Direct evidence for ethanol induced changes in CNS prostaglandins has been contradictory. Therefore, we developed a sensitive and specific assay based on selected- ionmonitoring, electron-capture negative ionization GC/MS detection of the N-methyl methoxime, pentafluorobenzyl ester, tris-trimethylsilyl ether derivatives of PGE2, PGE1, PGF1a, and 6-keto-PGF1a were below 15pg/mL in lumbar CSF of healthy humans and abstinent alcoholics. In order to investigate other means of measuring CNS prostaglandins, we explored both in vivo microdialysis techniques and in vitro tissue slice techniques. Extracellular fluid concentrations of PGE2, PGD2a, 6-keto-PGF1a and TXB2 were sampled from rat brain in vivo using microdialysis. The lowest levels measured may represent baseline in vivo production of eicosaniods in the central nervous system, whereas the higher levels present in the initial sampling period were believed to be due to the acute penetration injury of the microdialysis probe. Extension of the methodology o unanesthetized animals may provide a useful model for measuring in vivo effects of ethanol on eicosanoid production in the central nervous system. Results with in vitro tissue slice preparations of rat frontal cortex, showing no significant difference in eicosanoid production between control and ethanol exposed tissues, must be rationalized with behavioral studies showing significant attentuation of thanol's central nervous system effects following administration of eicosanoid synthesis inhibitors. The tissue slice data indicate that a simple enzymatic stimulation of eicosanoid production by ethanol does not occur, in vitro.